The humidification of dry air normally occurring in buildings during the winter heating season, and the cooling of hot summer air in arid areas by the evaporation of water thereinto, depends upon the efficient evaporation of water from the continuously wetted surfaces of an evaporative element or pad as, for example, an interstitial body having extensive surfaces to provide a large area of contact of the air with water. The air to be humidified or cooled is forced through the openings of the element where it contacts the wet baffles or fibers of which the evaporative element is composed. Exposure of relatively large water surfaces in this way results in the evaporation of large amounts of the water.
Regardless of the particular purpose for bringing the gas and liquid into contact with each other, it is always desirable in this type of apparatus to expose the largest possible liquid surface to the gas. For a given gross surface of the structure of an evaporative element, evaporation efficiency depends upon the proportion of the surface that is kept continuously wetted so that the largest possible surface of the liquid to be evaporated will continuously be exposed to the gas for evaporation. The invention is directed to this particular aspect of evaporator efficiency.
Many types of evaporative cooling and humidifying devices have been developed which utilize a gas-liquid contact unit of some sort held in position by any one of a number of means, which contact unit is water wetted by gravity feed or liquid immersion, and through which air is forced by a fan or the like.
U.S. Pat. No. 2,637,540, assigned to a common assignee, discloses such a device wherein a gas-liquid contact unit is positioned in a suitable frame. Water drips down onto the unit from a gutter-like trough and spreads therethrough. A fan forces air through the unit for cooling and humidifying purposes. Any water which drips from the bottom of the contact unit may be collected in a sump or the like and recirculated, if desired.
A number of different pad constructions are disclosed in that patent. Basically, the pad comprises a plurality of superposed, expanded sheets of water-absorbent character, the sheets being formed by cutting spaced, staggered slits and then expanding the sheet transversely of the slit length to form webs or baffles separated by openings. The sheets may be made of a water-absorbent, unbleached kraft paper which may be impregnated with a small amount of water resistant substance to improve its wet strength.
Pads constructed from expanded paper so treated have been marketed successfully by the inventor's assignee as well as other manufacturers for a number of years. These water-absorbent pads are sometimes reinforced by a sheet or sheets of generally flexible, non-absorbent material. For example, metal screening or expanded metal or plastic sheets may be placed between the superposed paper layers or on the outer faces thereof. Stitching, penetrating spikes, bonding or other means may be used to hold the several sheets of the flexible gas-liquid contact unit together.
Unfortunately, it has been found that while the non-absorbent supporting reinforcement components prevent sagging or bowing of the saturated kraft paper components in the evaporative element, their non-wicking ability affects the evaporative efficiency of the composite wicking pad.
The present invention is based on the discovery that a gas-liquid contact pad may be fabricated so that the evaporative efficiency of the pad is substantially increased, while still maintaining the desired dimensional stability and structural integrity properties. This is accomplished by alternating layers of slit and expanded water-absorbent or wettable rigidifying material, such as kraft paper, with layers of slit and expanded wicking material.
It is a principal object of the invention to provide a combination paper wicking pad having an upgraded evaporative efficiency.
It is another object of the invention to provide a liquid-gas contact pad having a substantially rigid and self-supporting structure whose inert strength and integrity is not impaired by long, continuous exposure to liquid.
It is a further object of the invention to provide a water-absorbent element which channels more water to and is more uniformly wetted in all areas of the element.
Still another aspect of the invention is to provide a more efficient evaporative element produced with a price reduction with no expected loss in performance.
Moreover, another object of the invention is to provide a hybrid kraft paper and wicking paper lamination which possesses greater dimensional stability than prior art liquid-gas contact pads.
It is also an object of the invention to provide a humidifier pad having high water absorption and wicking behavior.
It is an important object of the invention to provide a method of substantially increasing the evaporative efficiency of an evaporative pad formed from two different types of slit and expanded water-absorbent or wettable paper.
It is a related object of the invention to provide a method of making an evaporative wicking pad by adhesively securing overlying layers of slit and expanded water-absorbent paper.
In one aspect of the invention, a gas pervious liquid-gas contact pad comprises a reticulate body of wettable material having a large area of surfaces exposed. The contact pad comprises a plurality of slit and expanded sheets of wicking material, and a plurality of slit and expanded sheets of wettable kraft material. An arrangement is provided for connecting the sheets of the wicking material and the wettable kraft material in superposed and alternating relationship with one another to define a laminated, self-supporting, evaporative element. In the preferred embodiment, the composition of the wicking material is substantially 55% alpha bleached soft woods, 20% bleached soft woods and 25% bleached hard woods. The composition of the kraft material is substantially 47% soft woods and 53% hard woods. The basis weight of the wicking material is approximately 70 lbs. while the basis weight of the kraft material is approximately 41 lbs. or 120 lbs. The wicking material has a Klemm strip rise of about 100 millimeters per 2 minutes while a 3% resin-impregnated kraft material has a Klemm strip rise of 22 millimeters per 2 minutes, and a 15% resin-impregnated kraft material has a Klemm strip rise of 34 millimeters per 2 minutes.
In another aspect of the invention, an evaporative element for a humidifier or the like comprises a series of stacked layers of slit and expanded wicking paper, each of the layers of the wicking paper having a first evaporative efficiency, and a series of stacked layers of slit and expanded wettable kraft paper, each of the layers of kraft paper having a second evaporative efficiency. An adhesive arrangement is provided for securing the layers of wicking paper and wettable kraft paper together in continuous overlying and alternating relationship with one another to define a laminated evaporative element having a combined evaporative efficiency which is substantially greater than the average of the first evaporative efficiency and the second evaporative efficiency.
The invention also contemplates a method of substantially increasing the evaporative efficiency of an evaporative contact pad formed from a series of stacked layers of slit and expanded wettable rigidifying paper. The method comprises the step of securing the layers of rigidifying paper in contiguous, overlying and alternating relationship with a series of stacked layers of slit and expanded wicking paper to define a self-supporting, laminated evaporative contact pad.
The invention further contemplates a method of making an evaporative wicking pad comprising the steps of: slitting and expanding a series of layers of wicking material; slitting and expanding a series of layers of wettable kraft material; and securing the layers of wicking material and the layers of kraft material in contiguous, overlying and alternating relationship with one another to define a laminated evaporative wicking pad.